I'm looking forward to emulate the behavior of OS X Dock Stacks so that I can have, for instance, one stack for browsers and another one for IDES.
People at ask ubuntu are doing a lot of cleaver stuff with custom Launchers and Quicklists (see List of custom Launchers & Quicklists for Unity).
So has anyone figured out how to have stacks in Unity? Anything fancier than a static Quicklist over a dummy folder icon?

You can put just about anything in a drawer by drag and drop. You can even nest drawers inside one another. See below for a screenshot. It's been submitted to the software center but is awaiting review.